Analysis elements for analyzing a specific component in a liquid sample are known. For example, JP-A-2-150751 (corresponding to JP-B-7-21455) discloses an analysis element comprising a support having a through-hole, a porous film to which a reagent liquid containing light-reflecting insoluble particles has been applied and dried to form a reagent layer, the porous film being fixed on the support to cover the through-hole, and a sample holding layer fixed on the support to cover the reagent layer (the terms "JP-A" and "JP-B" as used herein mean an "unexamined published Japanese patent application" and an "examined Japanese patent publication", respectively). In JP-A-2-150751, titanium oxide is used as light-reflecting insoluble particles which, when whole blood is applied to the element and observed from the support side, hide red blood cells from view and also cut off light.
Titanium dioxide particles are white particles which reflect light with little absorption and are hardly dissolved in all kinds of solvents. They have a broad particle size distribution from fine (0.001 .mu.m) to coarse (1 mm or even greater). The smaller the particle size, the more liable to aggregation. Titanium dioxide particles are usually used in paints, ointments, cosmetics, and the like for making use of their opaqueness.
Since titanium dioxide particles are insoluble in a solvent and also liable to aggregate, they easily form lumps and precipitate in liquid, failing to provide a liquid system having a uniform concentration distribution throughout the liquid.
Therefore, in the preparation of an analysis element for analyzing a specific component in a liquid sample, a titanium dioxide dispersion (reagent liquid) undergoes aggregation and precipitation and cannot be applied to a substrate (porous film) uniformly. Such a disadvantage may be eliminated by adding a polymer or a thickener to make the reagent liquid viscous or by stirring the liquid. However, a liquid having a viscosity enough to prevent titanium dioxide particles from precipitating would have insufficient fluidity for easy application to a substrate and also deteriorate analysis precision of the analysis element. The stirring of a reagent liquid is accompanied by air entrapment. Once air bubbles are formed, they remain in the coating layer even after drying or burst to leave craters after drying.
The aggregation of titanium dioxide particles also proceed while the coating layer is being dried, making the surface of the coating layer non-uniform. When the titanium dioxide-containing layer serves as an optical reflecting layer, such non-uniformity of the surface causes non-uniform light reflection and seriously reduces the performance of the reagent layer. It has therefore been demanded to develop a technique for dispersing insoluble particles, such as titanium dioxide particles, in liquid uniformly without involving such an operation as might impair coating precision, i.e., stirring, and increasing the viscosity of the liquid more than necessary.